Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The novel eCell system maintains the activity of the entire repertoire of metabolic <em>E. coli</em> enzymes in cell-free protein synthesis. We show that this can be harnessed to produce proteins with selectively <sup>13</sup>C-labelled amino acids from inexpensive <sup>13</sup>C-labelled precursors. The system is demonstrated with selective <sup>13</sup>C-labelling of methyl groups in the proteins ubiquitin and peptidyl-prolyl <em>cis&ndash;trans</em> isomerase B. Starting from 3-<sup>13</sup>C-pyruvate, <sup>13</sup>C-HSQC cross-peaks are obtained devoid of one-bond <sup>13</sup>C-<sup>13</sup>C scalar couplings. Starting from 2-<sup>13</sup>C-methyl-acetolactate, single methyl groups of valine and leucine are labelled. Labelling efficiencies are 70 % or higher, and the method allows to produce perdeuterated proteins with protonated methyl groups in residue-selective manner. The system uses the isotope-labelled precursors sparingly and is more readily scalable than conventional cell-free systems.

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